Report Investigation of gas blowout on Snorre A - Well Integrity ...

SUMMARY
On 28 November 2004, an uncontrolled situation occurred during work in Well P-31A on the
Snorre A facility (SNA). The work consisted <strong>of</strong> pulling pipes out <strong>of</strong> the well in preparation
for drilling a sidetrack. During the course <strong>of</strong> the day, the situation developed into an
uncontrolled <strong>gas</strong> <strong>blowout</strong> on the seabed, resulting in <strong>gas</strong> on and under the facility. Personnel
who were not involved in work to remedy the situation were evacuated by helicopter to
nearby facilities. The work to regain control over the well was complicated by the <strong>gas</strong> under
the facility which, among other things, prevented supply vessels from approaching the facility
to unload additional drilling mud. After having mixed mud from the available well fluid
chemicals, this was pumped into the well on 29 November 2004, and the well was stabilized.
With the well stabilized and the <strong>gas</strong> flow stopped, the work to secure the well with the
necessary barriers could commence.
The PSA characterizes this incident as one <strong>of</strong> the most serious to occur on the Norwegian
shelf. This is because <strong>of</strong> the potential <strong>of</strong> the incident, as well as comprehensive failure <strong>of</strong> the
barriers in planning, implementation and follow-up <strong>of</strong> the work on well P-31A. Only chance
and fortunate circumstances prevented a major accident with the danger <strong>of</strong> loss <strong>of</strong> many lives,
damage to the environment and additional loss <strong>of</strong> material assets.
The consequences <strong>of</strong> the incident are costs related to delayed production, comprehensive and
time-consuming work to secure the well, normalization and start-up <strong>of</strong> the facility. Surveys
<strong>of</strong> the seabed after the incident revealed several large craters near the well template and near
one <strong>of</strong> the fastening anchors for the Snorre A platform. Three months after the incident,
production <strong>of</strong> oil and injection <strong>of</strong> <strong>gas</strong>/water had still not returned to normal levels. There
were no physical injuries in connection with the incident.
SNA is an integrated living quarters, drilling and production facility permanently anchored to
the seabed with tension legs. Under the SNA is a well template with 42 wells with risers and
several export lines. Total oil production from SNA is approx. 200,000 bbls/day. Under
slightly different circumstances, the incident could have resulted in (1) ignition <strong>of</strong> the <strong>gas</strong> and
(2) buoyancy and stability problems, with resulting danger <strong>of</strong> the loss <strong>of</strong> many lives, damage
to the environment and additional loss <strong>of</strong> material assets.
On 29 November 2004, the PSA appointed an investigation group to chart the course <strong>of</strong> the
incident, identify potential breaches <strong>of</strong> the regulations, as well as propose use <strong>of</strong> policy
instruments and recommendations for additional follow-up. The mandate included
circumstances up to when the well pressures in P-31A were stabilized at 10:22 a.m. on 29
November 2004. A task force was also designated to monitor the normalization work.
The investigation group has interviewed relevant personnel from the land organization and on
the facility, evaluated the submitted documents and conducted an inspection on the facility.
An MTO (man-technology-organization) diagram to map direct and underlying causes was
prepared to assist in analyzing the incident.
The regulations require technical, operational and organizational barriers that both prevent
serious incidents from occurring and that they escalate. Serious failures and deficiencies have
been uncovered in all phases <strong>of</strong> Statoil's planning and implementation on well P-31A. These
relate to:
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